The present invention relates to switching power supplies, and more particularly, to a charge pump switching power supply with voltage regulation at its input.
Portable electronic devices are ubiquitous, and are increasing in both number and diversity. Examples include cellular telephones, personal digital assistants (PDAs), portable computers, portable tape/CD/MP3 players, hand-held televisions, and the like. These portable devices are generally powered by a battery, which may be rechargeable, such as nickel cadmium, nickel metal hydride, or lithium ion, or which may be of a single-use type, such as conventional alkaline cells. All of these batteries lose their charge over time, and consequently do not produce a single, constant voltage output.
To simplify the design of the electronics operating on battery power, the time-varying output voltage of the battery must be stabilized, or regulated, to a constant, predetermined value. In particular, as the battery charge decays, its output voltage may fall below the required operating voltage of the electronics, necessitating a xe2x80x9cboost,xe2x80x9d or increase of the battery""s voltage. One way to boost an input voltage, such as that from a battery, to a higher output voltage is by use of a type of switching power supply known generally in the art as a charge pump. A charge pump typically contains one or more charge storage capacitors, also known in the art as bucket capacitors or boost capacitors, whose interconnection configuration relative to the input and output nodes and a circuit ground is configurable via a network of switches.
A charge pump is often preferable to a linear voltage regulator as a power source for electronics due to its efficiency, and its ability to boost voltages from input to output. A charge pump may be preferred over a switched mode power supply based on reactive elements due to its ease of use, relatively low noise, and lower cost. Factors that have prevented the widespread use of traditional charge pumps as previously known in the art include poor efficiency and limited output load current.
The present invention relates to a type of switching power supply generally known in the art as a charge pump. The switching power supply is connected in series between a power source, such as a battery, and a load to provide a generally constant output voltage to the load. The switching power supply comprises a switching circuit, a control circuit, and an input protection circuit. The switching circuit comprises a network of switches and charge storage capacitors, also known in the art as bucket capacitors. The switches of the switching circuit are selectively actuated under the direction of the control circuit to charge and discharge capacitors within the switching circuit to provide a regulated voltage at the output of the switching circuit. The regulated output voltage is fed back to the control circuit, which controls the operation of the switching circuit. The control circuit compares the output voltage with a reference voltage and generates a signal that controls the operation of the switching circuit. The input circuit has a plurality of modes that provide different ratios of input to output voltage.
An input circuit is connected in series between the power source and the input of the switching circuit. The input circuit serves three functions: 1) to prevent voltage breakdown of the switches in the switching circuit; 2) limiting currents from the power supply during switching transitions; and 3) preventing current reversal through the input of the switching circuit during switching transitions.